Spatial patterns of vascular plant diversity were studied in an unmanaged temperate forest in northern Spain. Diversity in 102 plots of 400 m(2) was analyzed against environmental and spatial variables. The Principal Coordinates of Neighbor Matrices method was used to create spatial variables that represent spatial structures on multiple scales. Variation partitioning on multiple regression was used to discover pure environmental and spatial fractions and their joint effects on diversity. Additionally, we created maps of the response and some explanatory variables to interpret their patterns. The results show that diversity is heterogeneously distributed in the basin and is explained mainly by environmental factors. Leaf litter cover proved the most important environmental factor. The spatial variables play an important role in structuring the environment but the low amount of variance explained by these when the effect of the environment is removed points to the lesser importance of neighborhood relations to the distribution of diversity values.